1. Field of the Invention
The present invention relates to photoconductors for electrophotography, and particularly to photoconductors having excellent physical characteristics and indicating high sensitivity with respect to light of a long wavelength of around 800 nm.
2. Description of the Prior Art
As conventional photoconductors for electrophotography, such a photoconductor wherein a selenium (Se) film 12 of around 50 .mu.m is formed on a photoconductive substrate 11 made of, for instance, aluminum or the like in accordance with vacuum deposition method as shown in FIG. 1 has been proposed. In this case, however, there are such disadvantages in that about one hour is required for the selenium deposition and that the Se photoconductor has sensitivity of a wavelength of only up to around 500 nm. As shown in FIG. 2, there has been also proposed another photoconductor in which a Se layer 22 of around 50 .mu.m is formed on a photoconductive substrate 21, and a selenium-tellurium (Se-Te) alloy layer 23 of several .mu.m is further formed thereon. In this photoconductor, the higher Te content in the above Se-Te alloy results in the higher spectral sensitivity, in other words, such sensitivity extends up to long wavelength, whilst whose surface charge retention characteristics become inferior with increase in amount of Te added, and thus it brings about such a serious problem that the photoconductor of this type cannot actually be utilized as a photosensitive material. FIG. 6 is a graphical representation illustrating spectral sensitivity of a layered photoconductor system which is prepared, as described in detail hereinbelow, by forming a Se layer having 50 .mu.m thickness on an aluminum substrate, and further forming 3 .mu.m Se-Te alloy consisting of 85 mol% of Se and 15 mol% of Te thereon. In this case, the amount of Te added is substantially limited to such extent as described above, besides this photoconductor system has sensitivity of up to only around 700 nm (curve C').
Furthermore, there has been proposed a photoconductor of so-called separated function type as shown in FIG. 3 which consists of a carrier generation layer 32 prepared by coating chlorodianeblue or a squaric acid derivative on an aluminum substrate 31 with a thickness of around 1 .mu.m and a carrier transport layer 33 formed by coating a mixture of polyvinylcarbazole or a pyrazoline derivative of high insulation resistance and polycarbonate resin on the carrier generation layer with a thickness of 10-20 .mu.m. Spectral sensitivity characteristics of such separated function type photoconductor are determined on the basis of characteristics of the aforesaid carrier generation layer. In this respect, however, it is actual circumstances that such type of photoconductor has no sensitivity with respect to light of 700 nm or more at present.
Recently, various attempts have been made to utilize semiconductor laser as light source in a laser beam printer or the like wherein laser light is utilized as its light source and a photoconductor for electrophotography is employed. In this case, since wavelength of such light source as described above is around 800 nm, such a photoconductor having characteristic properties of high sensitivity with respect to long wavelength light of around 800 nm is strongly requested.